1. Field of the Invention
This invention relates to a substrate transportation device. More specifically, the present invention relates to a substrate transportation device for transporting a material, for example, a glass tray from one location to another, and providing sufficient support for the entire body of the tray, and thereby improving the transportation of the substrate in an efficient and timely manner.
2. Description of the Related Art
Automation and robotics are used in substrate transportation to improve the efficiency of transportation, and serve to reduce human contamination of the glass tray, used in the contamination-sensitive thin film transistor liquid crystal displays (TFT-LCD). Such a glass tray is manufactured in clean-room environments.
When a large glass tray is placed in a housing by a robotic apparatus, the tray must be supported underneath. This is often accomplished by a grid structure. As shown in FIG. 1, the grid structure is formed by rows of horizontally disposed pairs of supporting grids 80 that extend toward the center of the housing 10 from the inner walls of the housing. The grids 80 are vertically spaced to allow a glass tray 22 to be supported by each pair of grids. One of the purposes of having the grid structure only partially extending across the housing is to minimize contact with the surface of the glass tray and thereby reduce contamination. However, the arrangement of the existing grids in current housings causes the glass trays to droop or sag in the middle, because there is no support for the middle of the glass tray. Sagging of the glass trays causes the trays to become undesirably bent. Further, the sagging of the glass trays causes the trays to have a vertically concave cross section, resulting in glass trays that occupy a vertical space that is greater than the thickness of the glass tray. See FIG. 1. As such, fewer glass trays can be transported through the housing.
In order to increase the number of glass trays that can be supported as well as transported through the housing, another type of supporting system was developed. FIG. 2 illustrates supporting lines 82 for supporting the glass trays 22. The supporting lines 82 are shown as having end portions that are fastened to the inner walls of the housing 10 and span the width of the housing. Although each supporting line 82 supports the entire body of the glass tray, the weight of the tray causes the supporting line, and therefore the tray, to sag in the middle. Further, the supporting lines are arranged so close together that a robotic device cannot access, and thereby transport, the trays to and from the housing. In this arrangement, the glass trays must be transported by an axle system underneath each glass tray, which can only dispense the trays one by one.
Therefore, there is a need for an improved device and method for transporting a substrate that minimizes contact with the housing, but supports both the ends and the middle of the substrate.